This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/JP01/01869 which has an International filing date of Mar. 9, 2001, which designated the United States of America.
1. Field of the Invention
The present invention relates to an injector made of synthetic resin.
2. Description of Related Art
There has heretofore been known an injector 31 of synthetic resin, as shown in FIG. 6 of the accompanying drawings, as a disposable injector, for example. The injector 31 comprises a barrel 4 of synthetic resin having a luer taper fitting 3 for mounting an injection needle 2 thereon, and a plunger 5 of synthetic resin having on its tip end a gasket 32 held in intimate sliding contact with an inner wall surface 4a of the barrel 4. The plunger 5 is made of polypropylene, polystyrene, polycarbonate, or the like, and has a crown-shaped projection 34 on its tip end which has a radially projecting flange 33.
The gasket 32 is complementary in shape to the crown-shaped projection 34, and is snugly fitted over the crown-shaped projection 34. The gasket 32 includes a sliding ridge 35 positioned radially outwardly of and aligned with the crown-shaped projection 34, and is made of an elastic synthetic resin so that the gasket 34 can be held in intimate sliding contact with the inner wall surface 4a of the barrel 4. When a medicine is drawn into the barrel 4, the plunger 5 is pulled to develop a negative pressure in the barrel 4. At this time, since the gasket 32 is securely locked on the flange 33, the gasket 32 is prevented from being detached from the crown-shaped projection 34 under the negative pressure.
The conventional injector 31 shown in FIG. 6 is disadvantageous in that the overall length of the injector 31 is large because of the projection 34 that is constructed to prevent the gasket 32 from being dislodged out of position. The gasket 32 fitted over the projection 34 is made of a material which is different from the material of the projection 34. Therefore, the gasket 32 and the projection 34 need to be prepared separately and then combined together subsequently.